Posted
by
timothy
on Friday December 31, 2010 @05:08AM
from the new-breed-of-calculator-watches dept.

cylonlover writes "In a new, more efficient approach to solar powered microelectronics, researchers have produced a microchip which directly integrates photovoltaic cells. While harnessing sunlight to power microelectronics isn't new, conventional set-ups use a separate solar cell and battery. What sets this device apart is that high-efficiency solar cells are placed straight onto the electronics, producing self-sufficient, low-power devices which are highly suitable for industrial serial production and can even operate indoors."

As a CS student about to graduate and applying for grad schools, I hope I can answer this one pretty easily:

put the entire chip beneath a glass/etc protector of some kind, since photovoltaic uses photons(which pass through glass/etc) shouldn't be much issue , IANA(chemist/physicist)... so I think this is right

and for the use... that one I'm more sure on, many possible ideas pop to my mind, environmental sensors of some kind... temp, chemical, moisture, etc.... have this chip as the collection and storage (r

Hmm... provided you could build some capacitance into the die, it would be trivial to manufacture, en-masse, an array of incredibly inexpensive devices that could respond to a light-signal stimulus, much the same way that RFID tags respond to a suitable RF signal.

I can't think of an immediate application, but the key technical difference would be that you can transmit focussed, directional light in a laser, which is a much more difficult and wasteful feat with RF. You could therefore elicit a response from

Capacitance definitely makes it more interesting, because the device can store energy for a period, and then use it in a short burst. The instantaneous current can be greater than supplied by the cell, so it could transmit things etc.

The exposure was my first thought as well, but from an electrical standpoint. A solar cell is just a diode with a large junction area, as I understand it, and most semiconductors are light-sensitive, so it didn't seem you'd want them exposed to intense light that causes currents to be generated throughout the circuit. But here they put the traditional circuitry on a layer below the solar cell. Still, as you note, the solar panel is so small that it generates very little power. If you increased its area, you'd increase the area of the underlying layer as well, which seems it'd increase its cost. Sure, it wouldn't have circuitry in the entire area, so the defect rate wouldn't scale as badly as it does for normal large chips, but it still seems it'd be cheaper to just use a separate solar panel of whatever size is needed. Maybe this would have a really specialized use.

Indeed, many years ago I built an experimental bidirectional fiber-optic
link simply by gluing LEDs to each end of a short (3m) plastic optical fiber.
(I ground down each LED close to its chip, then polished it and glued
it with clear epoxy.)
When not powered, the LED would act as a photodiode.
It wasn't very fast - the slow response of the circuit I used to amplify
the weak current limited it to perhaps 100KHz. But it worked.

There is a small revolution in progress for "energy harvesting" technology. Where micro watt level power generation is just fine. This is an obvious next step that will reduce chip count. Already waiting for data sheets.

If you used a solar cell as a light sensor, it'll deliver just a few milliwatts that you'd have to amplify anyway.With this technology, you could place one of these cells on top of an amplifier, and apply power to the whole thing. It would then give you a reading of ambient light in a more reasonable range (say from 0V to V+), straight from the chip.

This could be useful as a one chip light sensor, say for a digital camera.

It could be good for a pre-amp on a sensor signal which absolutely must be as isolated as possible... eliminating noise on the power line.

If the light it was powered by had any brightness modulation, it would pick that up as power supply noise as well, so you need a filter on the power supply regardless. Common examples of modulated light are LED and fluorescent, which are quite common.

The important question to ask is, "what could such a chip be economically used for?"

Unless one is developing something for military or other national security-type purposes, where cost is typically significantly less important than attaining the ultimate in performance (however "performance" is defined in the application), the question typically is, "what's the cheapest way to do X?"

If, as is frequently the case, X is defined as "power the chip," one has an interesting economic quandary: In terms of money/area, conventional solar cells, especially amorphous solar cells, are about the cheapest form of silicon known to man. Using this new technology, though, these solar cells would be replaced by area on an integrated circuit, which is about the most expensive form of silicon known to man. Worse, the power consumed by the electronics must be minimized ("below 1 milliwatt"), so one is pressured into using very fine-lithography silicon, which is the most expensive form of silicon known to man.

The only way I can see that one wins on cost with this technology is if one has electronics that are so low-powered that they can be powered by an amorphous solar cell with an area equal to that of the circuitry itself. If you need a point of reference on the practicality of this requirement, I point you to your average solar-powered calculator, which has a solar cell area of several cm^2, and an active circuit area of probably less than 5 mm^2.

If, however, X is defined as "power the chip with a monolithic structure," perhaps for acceleration, board area, or other system-level requirements, then using external solar cells is prohibited (by the terms of the game), and then this technology begins to look more appealing. Even then, however, I would wonder if it wouldn't be easier to use chip stacking [siliconfareast.com] or similar technology to put a solar cell on a chip, since then each die could be processed in a manner optimum for its purpose (solar cell or integrated circuit). And, of course, you're still left with the problem of getting sufficient power from such a small area.

As an earlier poster pointed out, much larger defects can be tolerated on the photovoltaic portion ("they put the traditional circuitry on a layer below the solar cell") so the costs would not be expected to be as astronomical as if the electronics were side by side with the photovoltaic portion with a very small allowable defect size. If it was side by side you'd expect the sort of costs that prevent us all from having 35mm digital backs on our cameras (whopping big bit of very expensive silicon vs a much

The only way I can see that one wins on cost with this technology is if one has electronics that are so low-powered that they can be powered by an amorphous solar cell with an area equal to that of the circuitry itself. If you need a point of reference on the practicality of this requirement, I point you to your average solar-powered calculator, which has a solar cell area of several cm^2, and an active circuit area of probably less than 5 mm^2.